1. Field of the Invention
The present invention relates to a display device and a method for manufacturing the display device provided with an electrophoretic display element for displaying images in such a manner that fine particles dispersed in a solvent is made to move or rotate according to voltage application to an interposed electrode so that the reflectivity is changed. The present invention relates to, in particular, an electrophoretic display device and the method for manufacturing the electrophoretic display device which is formed by combining an electrophoretic display element and a thin film transistor (hereinafter, referred to as a TFT) in which a channel region is formed using a microcrystalline semiconductor.
2. Description of the Related Art
In recent years, electronic paper (also referred to as digital paper or a paper like display) is attracted attention and some of it is put into practical use. The form that the electronic paper finally aims is as follows: the form which is thin, has high visibility, is rewritable, and holds display even after power is turned off.
In a technique of the electronic paper, a method in which an image is displayed using a phenomenon promoting movement and rotation of particles by an electric field is referred to as an electrophoretic method. The electronic paper in the electrophoretic method (hereinafter, referred to as an electrophoretic display device) is disclosed in patent document 1 (Japanese Published Patent Application No. 2006-251093). According to patent document 1, a thin film transistor (TFT) is used as a switching element for controlling the voltage between electrodes in each pixel. As a switching element, a thin film transistor using an amorphous semiconductor film (amorphous silicon or the like), a thin film transistor using a polycrystalline semiconductor film (low temperature polysilicon or the like), or the like is used. Note that as a method for forming a polycrystalline semiconductor film, there is a known technique in which a pulsed excimer laser beam is shaped into a linear laser beam by an optical system and an amorphous silicon film is crystallized by being irradiated while being scanned with the linear laser beam.
As described in patent document 1, a thin film transistor using a polycrystalline semiconductor film has advantages that mobility is higher than that of a thin film transistor using an amorphous semiconductor film by two or more digits, and a pixel portion and a peripheral driver circuit of an electrophoretic display device can be formed over one substrate. However, the thin film transistor using a polycrystalline semiconductor film requires a more complicated process than the thin film transistor using an amorphous semiconductor film because of crystallization of the semiconductor film. Thus, there are problems such as a reduction in yield and an increase in cost.